Some superb action across Europe this weekend featured red cards, surprise resignations, surprise results, an unlikely title challenger and a dangerous French reunion.

Here is what caught our eye Around Europe this week:

Diego Costa treads a fine line

If ever a player embodied the win-at-all-costs mind-set of his coach, it’s Diego Costa at Chelsea. The Blues striker was at the heart of Chelsea’s vital 2-0 win over Arsenal, but not because he scored or played a part in either of the goals. His input came just before half-time, when he struck Laurent Koscielny in the face and then chest-bumped the Frenchman to the ground when confronted.

One red and one yellow card offense, within five seconds, and Costa was shown neither. Then Koscielny’s teammate Gabriel Paulista joined in, and Costa tangled with him, appearing to scratch him on the neck. Another possible yellow? Nothing. From the next move, Gabriel, clearly riled by Costa, flicked out his foot and it was enough for the Arsenal man to be sent off. As he walked off, Costa even had the nerve to shake his head with the air of a disappointed parent.

“Man of the match, for me,” he said, clearly trying to wind up Arsene Wenger. “To win derbies, you must have emotional control. If you forget that, you don't win ... I repeat every derby: you don’t win without emotional control, it’s a basic thing of the game.”

Wenger is right to feel hard done by but talking about it after the game only gives Mourinho more ammunition (he got in plenty more digs to Wenger, not the least of which was saying that Arsenal has the squad to be champion). Costa has been charged with violent conduct by the FA and could receive a retrospective card and ban, which would be his second this year: his first came when he evaded detection following a stamp on Liverpool’s Emre Can.

As Oliver Kay pointed out in The (London) Times, “it is hard to avoid the conclusion that Arsenal, more than most, could do with at least a little of the Chelsea forward’s nastiness”. Chelsea was desperate for a win to kick-start its season. That it came through Costa’s Machiavellian deviousness might please Mourinho even more. We can expect more of the same from Costa in future. It appears that no English referee wants to be the first to send him off.

Marseille fans ruin Valbuena's return

Mathieu Valbuena was public enemy numéro​ un on his return to Marseille wearing Lyon colours Sunday night, but even he might have been surprised by the vitriol directed his away at the Velodrome. After eight years at Marseille, he moved to Dinamo Moscow for a year and then returned to France to join Lyon. He never criticized Marseille, nor did it try to sign him. So for a start, the level of hatred was bizarre.

Marseille should expect punishment for its fans’ behavior: an effigy in his likeness hung from the stands, while bottles and projectiles were thrown his way whenever he took a corner (and also at Lyon goalkeeper Anthony Lopes). The situation was so bad that referee Rudy Bouquet took off the players after an hour and there was a 20-minute break for the situation to calm down.

​Marseille’s players seemed under instructions to target Valbuena: Romain Alessandrini was sent off for a two-footer on the winger and he might not have been the only one; Karim Rekik and Abdelaziz Barrada were fortunate not to go the same way.

Perhaps it would have been different if Remy Cabella had been shown a red and not a yellow for his early challenge on Christophe Jallet after 13 minutes.

As it was, Lyon was in control of the game and 1-0 up at the time of the stoppage. Lyon president Jean-Michel Aulas did not want his players to come out after the break, probably hoping his side would be awarded the win. Marseille president Vincent Labrune said that his club would take on responsibility, but added that the officials and Lyon must do the same. His implication was that Bouquet’s decisions—he correctly awarded a first-half penalty to Lyon—were in some way to blame for the fans’ dangerous response. He also claimed that Lyon is used to playing against ten men, while Marseille is more used to playing with 10 men. Expect a row between Aulas and Labrune, both outspoken, to rumble on this week.

Marseille was the beneficiary of the stoppage: coach Michel had another 20 minutes with his players and it looked a different team for the last passage of the game. Rekik equalised and Valbuena, of all people, came desperately close to winning it with a shot right at the death. In the face of fierce provocation, the French winger kept his head while others lost theirs. It was emotional control that even Mourinho would have been proud of.

Was Favre's resignation a surprise?

When Lucien Favre was appointed Borussia Mönchengladbach coach in 2011, the team was headed for relegation. This week, he has left the team bottom of the Bundesliga but having reached the Champions League for the first time in 37 years. Last week’s return did not end well, with a 3-0 defeat at Sevilla. In the league, this season has been even worse: six defeats in a row, the latest at Cologne Saturday, left Favre announcing his resignation to the press before telling his bosses: “I no longer feel I’m the perfect coach for Borussia Mönchengladbach. I'll never forget the eventful years with Borussia as my most beautiful and emotional as manager ... You will always remain in my heart.”

That kind of emotion was reminiscent of Jurgen Klopp’s situation at Dortmund last year—both were heroes at their clubs and maybe Favre didn't feel he could turn around the surprising early season slump. No one has quite worked out why Mönchengladbach is struggling so much: it lost two key players from lost season: Christoph Kramer, going back to Leverkusen after his loan spell, and striker Max Kruse joining Wolfsburg, but Favre has dealt with that before.

Maybe the better comparison would be with his previous club Hertha Berlin. He left there in September 2009 after seeing three important players—Andrej Voronin, Marko Pantelic and Josip Simunic—leave the previous summer and then going on a six-game run of defeats. Hertha ended that season going down. It’s unthinkable that Mönchengladbach will go the same way.

The club is currently in shock—it wanted to reject his resignation—and sports director Max Eberl is now lining up a replacement. Favre, meanwhile, joins Klopp as another top coach out of work.

Can Napoli go all the way in Serie A?

I wonder what Diego Maradona thinks now. The Argentine World Cup winner and captain, a Serie A winner with Napoli in 1988, laid into new coach Maurizio Sarri last week. “This Napoli team doesn't have a good style of play, or a defense that offers the peace of mind to be able to dream big,” he said. “This Napoli will struggle to finish in mid-table, I'm angry because they didn't deserve this downsizing.”

Napoli’s response? It beat Club Brugge 5-0 in the Europa League, and followed that up with another 5-0 win, this time over Lazio, Sunday. The Lazio win is a statement of intent from a side that’s finally getting to grips with its new coach.

When Sarri joined, he compared his situation to switching phones: it takes some time to work it all out, then you realize the new one is better. He might be right.

Lazio was the team that beat Napoli at the end of last season to deny its place in the Champions League qualifiers. Three months on, playing 4-3-3 with Lorenzo Insigne pulling the strings behind Gonzalo Higuain, Napoli was a different proposition. Sarri, who refused to react to Maradona, wants even more from his team. “We haven’t changed anything in terms of our footballing ideas, as we’ve only changed our positions on the field. I think in any group there is room for improvement.”

The next big test is next weekend, when Juventus play at Stadio San Paolo. Win that one, and Napoli could be a dark horse for what could be an open Scudetto race.

Two La Liga goalkeepers, differing fortunes

Keylor Navas's future didn't look good three weeks ago. Real Madrid wanted him out and only an admin cockup scuppered his move to United with David de Gea going the other way. Since then, though, Navas has been outstanding: Madrid has not conceded for five league games and the Costa Rican No. 1 was at it again Saturday, with three fine stops to help Madrid edge past Granada 1-0.

Over in Barcelona, pressure is growing on Marc Andre ter Stegen, who missed a cross which allowed Levante sub Victor Casadesus a goal in Barca’s 4-1 win. No big deal, maybe, but ter Stegen has twice been beaten from over 40 yards this season too, and Barcelona has only had two clean sheets in eight games this season.

The focus still remains on Ronaldo, still one goal away from the 500th of his career, and Messi, who assisted one, scored two and missed a(nother) penalty, but the fates of the two goalkeepers could be decisive as the season plays out.

Matthew Peters/Manchester United/Getty Images

Top three players of the week

Anthony Martial (Manchester United)

A first league start for United and two more goals for Martial, whose form is allowing everyone to forget about Wayne Rooney’s drought in front of goal. Martial made the difference for United at Southampton, with two fine strikes and an impressive partnership with Memphis. It’s not quite Ronaldo and Rooney from 2004, but it’s an encouraging start from the teenager.

Iker Casillas (FC Porto)

The Spanish goalkeeper came up big for Porto in O Clasico, the big game in Portugal against title rival Benfica. Casillas made two excellent first-half stops to deny Kostas Mitroglou and Luisao for the visitor. Andre Andre scored the winning goal to keep Porto top of the table.

Angel Correa (Atletico Madrid)

The Argentine forward scored with his first touch after coming off the bench, following a smart drop of the shoulder which bewildered his marker. The highly rated Correa then set up fellow sub Fernando Torres for a second. Correa is way down the pecking-order of Atleti strikers, as it has Griezmann, Vietto and Martinez, but this season could be a breakout one for him.

Top three goals of the week

Matt Ritchie (Bournemouth vs. Sunderland)

The winger came to the Premier League with a big reputation after an outstanding Championship campaign last year. You can see why: his technique on this chest-and-volley from outside the area was sensational. Bournemouth is already five points clear of joint-bottom Sunderland, and Ritchie is one to watch.

[youtube:https://youtu.be/IQmZ05x9n6o]

Mario Gaspar (Villarreal vs. Athletic Bilbao)

A long-range strike in Villarreal’s impressive 3-1 win over Athletic, defender Mario’s effort was the pick of the week in La Liga. Bravo!

Francesco Totti (Roma vs. Sassuolo)

He may not have struck it that cleanly. And he may have been offside. But this was goal No. 300 for Totti in a Roma shirt. After the game, a 2-2 draw with Sassuolo, Totti said he was “only really happy when Roma win”. Still, an incredible achievement for one of the few one-club men left in the game. He turns 39 next week. His teammate Mo Salah scored the better goal, but this one, his 244th with his right foot, was historic.